I checked this after reading your question, Ted. The Data directory has the full res images, and for the largest image from that orbit it says:

Wednesday, April 26, 2006 6:49 AM 697587740 h1607_0009_nd2.img

697 Mb. But I was mistaken in thinking it was Phobos, I assumed that without checking - the second set of images from 1607 are of Mars. Even so, the largest Phobos image on that orbit, the nd2 image, is 9548940 bytes. Your images are the "super-resolution" images which are a lot smaller.

I'm still exploring the Mars Express Phobos images. This, I think, is the highest resolution image yet, from orbit 756. The original file was 169 MB, but largely dark sky. I have played with the contrast a bit to brighten the terminator. Several blocks casting shadows can be found along the terminator.

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